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    <title>Document</title>
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    <script>
        //用于异步编程 文件IO 数据库IO 网络请求
        
        //实例化promise对象
        const p = new Promise(function(resolve,reject){
            setTimeout(() => {
                // let data = '数据库中的数据'
                // resolve(data)
                let err = '数据读取失败'
                reject(err)
            }, 3000);
        })

        //调用promise对象的then方法
        p.then((value)=>{
            console.log(value)
        },(err)=>{
            console.log(err)
        })


        

    </script>
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